1. Field of the Invention
The present invention relates to a running speed control device for a vehicle which controls vehicle running speed by driving a throttle mechanism for an internal combustion engine, and to an opening and closing state abnormality detecting device for detecting an abnormality of an opening and closing state detecting device which detects an opening and closing state of the throttle mechanism used by the running speed control device.
2. Related Art
Conventionally, a running speed control device for a vehicle is well-known, which includes a throttle state detecting device such as an IDLE switch for detecting an opening and closing state of a throttle mechanism such as a throttle valve of an internal combustion engine, a vehicle speed detecting device such as a vehicle speed sensor for detecting running speed of a vehicle, and a throttle driving device for driving the throttle valve so that a vehicle speed matches a target running speed responsive to the difference between the vehicle speed and target running speed and an opening and closing states detected by the IDLE switch during the running speed control.
In such a running speed control device for a vehicle, if the running speed control starts when the throttle valve is fully closed and the present vehicle speed is nearly equal to the target running speed, the throttle valve is opened by some degree to prevent temporary drop of the running speed due to the delay, and caused by the time required to move the throttle valve to a desirable opening position.
However, in such a running speed control device for a vehicle, if an IDLE switch fails and can not reliably detect that the throttle valve has opened, the following situation may be caused. For example, if the IDLE switch can not detect that the throttle valve has opened when the throttle valve is opened by some degree as described above, the throttle driving device continues driving the throttle valve toward an open side, because the control device determines that the throttle valve is fully closed. The drive of the throttle valve may go on until the vehicle speed becomes higher than the target vehicle speed. If so, the running speed of the vehicle overshoots and riding comfort of the vehicle deteriorates.